Electronic fuel injection system

ABSTRACT

Electrical signals corresponding to air valve position, the vacuum signal between the air valve and the throttle blade, and the intake manifold pressure determine the width of pulses applied to electrical fuel injectors located in the intake manifold. Pulse frequency is determined by an electrical signal generated by engine revolution. Electronic circuitry shortens the basic pulse width as a function of pulse frequency so fuel delivery is determined only by the above electrical signals.

ties Pa Robert S. Harrison;

Arthur R. Harris, Detroit, Mich. 798,650

Feb. 112, 1969 Apr. 20, 1971 Ford Motor Company Dearborn, Mich.

Inventors Appl. No. Filed Patented Assignee ELECTRONHQ FUEL lNJlEC'IlON SYSTEM 15 Claims, 4 Drawing Figs.

US. Cl l23/32EA, 123/1 19R llnt. Cl lFOZm 51/00 Field of Search .II l23/32(E), 32 12-1 119, 179

[56] References Cited UNITED STATES PATENTS 2,876,758 3/1959 Armstrong 123/1 79A 3,240,191 3/1966 Wallis l23/32E-1 3,250,262 5/1966 Allen 123/1 19 3,482,558 12/1969 Casey eta] 123/119X Primary ExaminerLaurence M. Goodridge Att0rneys-John R. Faulkner and Glenn S. Arendsen TRACT: Electrical signals corresponding to air valve position, the vacuum signal between the air valve and the throttle blade, and the intake manifold pressure determine the width of pulses applied to electrical fuel injectors located in the intake manifold. Pulse frequency is determined by an electrical signal generated by engine revolution. Electronic circuitry shortens the basic pulse width as a function of pulse frequency so fuel delivery is determined only by the above electrical signals.

ELECTRONIC FUEL INJECTION SYSTEM SUMMARY OF THE INVENTION Current electronic injection systems for reciprocating internal combustion engines use electrical pulses generated by engine rotation to actuate fuel injectors supplying fuel to the combustion chambers. An electrical signal generated by engine intake manifold pressure modifies the duration of the pluses and thereby attempts to relate the amount of fuel supplied to the engine to engine requirements. Additional signals responsive to engine temperature, ambient air temperature, barometric pressure, and air humidity usually are necessary in such systems to further modify pulse duration according to actual engine requirements during the many different phases sand climatic conditions encountered in normal engine operation. Although these electronicsystems are capable of improving fuel metering, the large number of signals necessary to sense the quantity of inducted air under the wide variety of climatic and operational conditions has increased the expense of the systems to an almost prohibitive level. Commercial versions of the systems therefore compromised many of these factors to achieve reasonable cost levels.

This invention utilizes electrical signals generated by the position of an air valve, the pressure signal between the air valve and a manually controlled throttle blade, and the intake manifold pressure to determine the amount of fuel supplied to an engine. These three sensing points produce signals proportional to the airmass flowing to the engine combustion chambers for all engine operating and climatic conditions and thus obviate the need for any additional signals. In the invention, an electrically actuated fuel injector is positioned where it will deliver fuel to combustion chambers of a reciprocating internal combustion engine. An air passage for delivering air to the combustion chamber contains a manually operated throttle blade for controlling the amount of airflow. Air flowing through the air passage positions an air valve located upstream of the throttle blade. Electrical elements are attached to the air valve, to a pressure sensitive device connected to the air passage between the air valve and the throttle blade and to a pressure sensitive device connected to the air passage downstream of the throttle blade. An electronic circuit produces pulses at a frequency determined by engine revolutions and shortens the pulse duration as a function of pulse frequency so the time integrated pulse area is independent of engine speed. The circuit then uses signals from the electrical elements to modify the basic pulse width according to the engine fuel requirements. These modified pulses are applied to the fuel injector which opens to deliver fuel to the engine combustion chamber during each pulse.

Fuel is supplied to the injectors at a pressure independent of engine speed. The injectors preferably are located in the engine intake manifold just upstream of the intake valves and are pulsed just prior to or during the intake valve opening operation. In multicylinder engines having the injectors located in the intake manifold, the injectors can be pulsed individually, in pairs, in sets of any higher number, or all at the same time. A streamlined air intake structure is used in the system to provide a low profile induction system and convenient pressure tapping points. Pressure signals from two of the above locations are combined inan idle mixture adjustment system to provide proper pulse widths during idling conditions.

Variable resistors serve conveniently as the electrical elements. One side of the resistance is connected to the ground terminal of a source of electrical energy, and the sensing element is connected by an electrically insulating material to the movable tap. The electronic circuit is connected electrically to the movable taps in a manner such that the final pulse width increases as the resistance between the taps and ground increases. With a constant injection pressure, fuel delivery from the injector depends on pulse area, and the resistances in the electrical elements are designed to produce the desired pulse width for each set of operating conditions. Variable capacitance inductance, or other electrical parameters can be used in place of the variable resistances to provide the necessary modulation of pulse width.

Cold starting enrichment is provided by a switch connected to a thermally positioned choke plate located upstream of the air valve. One switch terminal is connected to ground and the switch pole contacts that terminal when choke plate is closed to increase the resistance to ground according to an enriching resistance in series with the switch. A thermally variable enriching resistance provides extremely accurate control during cold starting, and even a constant enriching resistance greatly improves fuel economy and exhaust emission.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view of the air intake structure of this invention showing the external air valve linkage and the linkage connecting a temperature responsive means to the choke blade and throttle blade fast idle cam.

FIG. 2 is a schematic of the system showing a sectioned elevation of the air intake structure and the input circuits of the electronic controller.

FIG. 3 is a top view of the air intake structure with portions broken away to shown the idle adjustment system. The external linkage shown in FIG. 1 has been removed from FIG. 3 for clarity.

FIG. 4 is a schematic of the electronic circuitry of controller.

DETAILED DESCRIPTION Referring to FIGS. 1, 2 and 3, the air intake structure is indicated generally by numeral 10 and comprises a flange l2 fastened to a corresponding flange on the engine intake manifold (not shown). An oval conduit 14 made integrally with flange 12 contains an oval air passage 16 that makes a turn and connects with two circular air passages 18 and 20 located side-by-side in flange 12. Air passages 18 and 20 communicate with the air passage in the engine intake manifold.

Extending laterally through air passages Iii and 20 is a throttle shaft 22. Throttle plates 24 and 26 are mounted on shaft 22 within circular passages 18 and 20 respectively so clockwise rotation of shaft 22 open passages 13 and 20.

An air valve shaft 28 extends through air passage 16 and has its ends mounted rotatably in the conduit 14. Shaft 28 is parallel to and is mounted slightly above the major diameter of air passage 16. An air valve plate 30 is fastened to shaft 28 within air passage 16 so opening movement of the air valve rotates shaft 28 clockwise. Upstream of air valve shaft 28, a choke plate shaft 32 extends through passage 16. Shaft 32 is parallel to shaft 28 but is mounted slightly below the major diameter of air passage 16. A choke plate 34 is fastened to shaft 32 within air passage 16.

Referring primarily to FIG. 1, an L-shaped lever 36 is fastened to shaft 22 outside of flange i2. One leg of lever 36 carries a projecting table 38. A screw 40 is threaded into a boss 42 mounted on the exterior of conduit 14 with the end of screw 40 contacting tab 38 when the throttle blades are in the closed or idling position.

The other leg of lever 36 terminates near the stepped surface 44 of a cam member 46 pivotally mounted on conduit 14. A rod 48 connects cam member 46 with a lever 50 fastened to choke plate shaft 32. Another lever 52 is fastened to choke plate shaft 32 and is connected by a rod 54 to a conventional automatic choke mechanism containing both temperature and manifold pressure responsive devices. An example of such a choke mechanism is disclosed in US. Pat. No. 3,281,l30.

' A bellcrank S6 is fastened to air valve shaft 29 and has one leg connected by a rod 58 to a damping mechanism indicated generally by numeral 60. A typical damping mechanism is disclosed in US. Pat. application Braun et a1, Ser. No. 61 1,906, filed .Ian. 26, 1967, the entire disclosure of which is hereby incorporated into this specification. The other leg of bellcranlt 56 is connected by a tension spring 62 to an anchor 64 formed on the exterior of conduit 14. Spring 62 acts though bellcrank S6 to urge air valve plate into its closed position.

A passage 66 is drilled into the left side of flange 12 to communicate with passage 18 below the closed position of throttle blade 24. Pressed into the outer end of passage 66 is a tube 68 that connects passage 66 with one chamber 70 of a manifold vacuum motor 72. Motor 72 contains a flexible diaphragm 74 that separates chamber 70 from a chamber 76. A compressive spring 78 located in chamber 70 urges diaphragm 74 into chamber 76.

Projecting through chamber 76 and out of the left side of motor 72 is an actuating rod 80 made of an electrically insulating material. Rod 80 is connected to the movable tap 82 of a variable resistor represented by numeral 84. One terminal of the resistor element 86 of variable resistor 84 is floating and the other terminal is connected to a lead 87, With atmospheric pressure in passage 66, diaphragm 72 positions tap 82 near the floating terminal of element 86; decreases in the intake manifold pressure move tap 82 toward the terminal connected to lead 87.

Beneath conduit 14, a second passage 90 is drilled into flange 12 at the midpoint of the flange. Passage 90 intersects a pasage 92 drilled into flange 12 from the side, and a short vertical passage 94 connects the intersection point of passages 90 and 92 with air passage 16 between throttle plate 24 and air valve plate 30. Passage 94 has a small metering jet 96 pressed into its passage 16 end. A small sensing passage 98 connects passage 92 with passage 18 just below the idling position of throttle blade 24, and a threaded adjusting screw 100 is threaded into the open end of passage 92 so its tapered point 102 is movable through the intersection point of passages 92 and 98.

Referring primarily to FIG. 2, the open end of passage 90 has a tube 104 pressed therein. Tube 104 connects passage 90 with one chamber 106 of an air valve depression vacuum motor 108. A diaphragm 110 separates chamber 106 from a chamber 112 and a compression spring 114 positioned in chamber 106 urges the diaphragm 110 toward chamber 1E2. A rod 116 made of an electrically insulating material is fastened to diaphragm 110 and projects through chamber 112 and out of the vacuum motor housing where rod 116 is connected to the movable tap 118 of a variable resistor 120. Tap 118 is connected to lead 87. One tenninal of the resistor element 122 of resistor 120 is connected to ground and the other terminal is floating. With atmospheric pressure in passage 90, diaphragm 110 positions tap 118 near the grounded tenninal of element 122; decreases in the pressure move tap 118 toward the floating terminal. Chambers 76 and 112 are connected by a tube 125 to a balance port 126 opening into passage 16 upstream of choke plate 34. Port 126 faces upstream so an impact pressure is developed at high speeds.

Air valve shaft 28 is connected to the movable tap 128 of a variable resistor 130. One terminal of the resistor element 131 of resistor is floating and the other terminal 133 is connected to a switch arm 134. When air valve plate 30 is closed, tap 128 is positioned near terminal 133; opening movement of the plate moves the tap toward the floating tenninal of element 131. Choke plate shaft 32 is connected by an electrically insulating material to switch arm 134 that moves to contact either of two tenninals 135 and 136. Tenninal 135 is connected to ground through a resistor 137 and terminal 136 is connected directly to ground. Arm 134 contacts tenninal 135 when the choke plate is closed and contacts terminal 136 when the choke plate moves away from its closed position.

An electrical lead 138 connects tap 82 to one input terminal 140 of an electronic control indicated in FIG. 2 by numeral 142. Similarly, a lead 148 connects tap 128 to an input terminal 150. A third'input terminal 152 for control 142 is connected to any device 154 capable of producing a signal having a frequency representative of engine rpm. The output terminal 156 of circuit 142 is connected via an amplifier (not shown) to the electrical operating mechanisms of a plurality of fuel injectors 158.

The electronic circuitry shown in FIG. 4 consists of a monostable multivibrator capable of producing a square wave having a constant width enclosed by dashed line 160, a power supply capable of producing an output voltage inversely proportional to the frequency of the square wave enclosed by dashed line 162, and a monostable multivibrator capable of producing a variable pulse width enclosed by dashed line 164. A conventional automotive storage battery 166 has its negative plate connected to ground at 168 and its positive plate connected through a resistor 170 to a terminal 172. A Zener diode 174 has its anode connected to the negative battery plate and its cathode connected to terminal 172. Diode 174 insures a constant voltage at terminal 172 despite variations in the voltage provided by battery 166.

Referring to multivibrator 160, terminal 152 is connected through a capacitor 174 to the base of a PNP type transistor 180. Terminal 172 is connected through a resistor 182 to the emitter of transistor and through a resistor 184 to the base of transistor 180. A resistor 186 connects the base of transistor 180 to ground and a resistor 188 connects the collector to ground.

The emitter of transistor 180 is connected to the emitter of a second PNP type transistor 190. A capacitor 192 couples the collector of transistor 180 to the base of transistor 190. Resistors 194 and 196 connect the base and collector of transistor 190 to ground.

Resistors 182, 184, 186, 188, 194 and 196 are selected to reverse bias transistor 180 and forward bias transistor 190 into saturation in the absence of a signal at terminal 152. A negative pulse at tenninal 152 is applied to the base of transistor 180 to drive transistor 180 into its active region. Capacitor 192 couples the rising voltage at the collector of transistor 180 to the base of transistor 190, thereby reverse biasing transistor 190. Transistor 190 remains reversed biased until the charge on the right plate of capacitor 192 discharges through resistor 194 at which point transistor 190 again switches into conduction. The increased current through resistor 182 drops the voltage at the emitter of transistor 180 to begin turning transistor 180 off. Voltage on the left plate of capacitor 192 then drops to bias transistor 190 rapidly into saturation. With a constant supply voltage, the off time of transistor 190 depends on the RC constant of capacitor 192 and resistor 194, so each negative pulse at terminal 152 thus produces a negative going square wave pulse at the collector of transistor 190 that has a constant pulse width.

Turning to the variable voltage power supply circuit 162, tenninal 172 is connected to the collector of an NPN type transistor 202. A resistor 200 connects the collector to the base of transistor 202. The base of transistor 202 is connected through a resistor 204 to ground, and the emitter is connected to the emitter of a PNP type transistor 206. A resistor 208 connects the collector of transistor 206 to the base of transistor 202.

A resistor 210 connects the emitter of transistor 202 to a tenninal 212. Resistor 214 connects terminal 212 to the base of transistor 206, and a resistor 216 in parallel with a capacitor 218 connect terminal 212 to ground. A resistor 221 connects the collector of transistor 190 to terminal 212.

Transistors 202 and 206 are biased as linear amplifiers. Resistor 216 and capacitor 218 integrate the square wave from the collector of transistor 190 into a constant voltage inversely proportional to the pulse frequency. Resistor 214 applies the constant voltage to the base of transistor 206 to increase the conduction of transistor 206 in inverse proportion to the voltage. Increased conduction of transistor 206 increases the voltage at the base of transistor 202 to reduce the conduction of transistor 202. A constant voltage inversely proportional to the pulse frequency thus appears at the emitter of transistor 202.

Turning now to multivibrator circuit lltid, a resistor Z122 connects the emitter of transistor 202 to the emitter of a PNP type transistor 2241. A resistor 22b connects the emitter of transistor 202 to the base of transistor 224 and respective resistors 228 and 2% connect the base and collector of transistor 224 to ground.

The emitter of transistor 224i is connected by a resistor 23] i to the emitter of a second PNP type transistor 232 that has its collector connected to ground. Output terminal ass is connected to the emitter of transistor 232. A capacitor 236 couples the collector of transistor 22d to the base of the transistor 232. Terminals M and i 0 are connected to the base of the transistor 232.

Multivibrator circuit 11M operates in essentially the same manner as multivibrator circuit loll except that l the square wave appearing at terminal 156 has positive'going pulses rather than negative and (2) the width of the pulses increases with the resistances of the variable resistances connected to terminals M0 and 1150 but decreases with the voltage appearing at the emitter of transistor 202. These results occur in the following manner.

Transistor 22d normally is turned off and transistor Z32 normally is conducting, During conduction of transistor 232, a relatively low voltage appears at terminal H56. Each negative pulse at terminal i152 is applied to the base of transistor 224 and turns on that transistor. Capacitor 236 transmits the positive pulse then appearing at the collector of transistor 224 to the base of transistor 232 to reverse bias transistor 232. Transistor 232 remains reverse biased until the charge on capacitor 2% is dissipated through the resistances connected to terminals Md and ltStl to value that is a function of the voltage applied to the emitter of transistor 232. That voltage in turn is a function of the voltage at the emitter of transistor 202 which is inversely proportional to the pulse frequency. By proper selection of components, the voltage decreases at the emitter of transistor 202 cancel the effects of the frequency increases so the pulse width appearing at terminal R5! represents only the values of the resistors connected to terminals Mil and llfiti.

During engine cranking, choke plate 34 is closed by the automatic choke mechanism connected to rod M. Switch arm H34 contacts terminal 135 to couple resistor 137 between tap I28 and ground. Cranking produces a slight decrease in intake manifold pressure that opens air valve 30 slightly. A relatively high resistance thus appears between terminal 154) and ground to widen the pulses applied to injectors b. The high manifold pressure acts via vacuum motor 72 to position tap 82 near the floating end of resistor ttti. A pressure intermediate the manifold pressure and the atmosphere is sensed by vacuum motor ll that positions tap M8 at an intermediate location on resistor 122. Virtually all of resistor as and part of resistor H22 thus are in series with tap b2, and this high resistance also widens the pulse width.

When the engine starts, passage as applies the decreased manifold pressure to diaphragm M, which moves tap 82 toward the lead W end of resistance as. At the same time choke plate M is pulled open by the automatic choke mechanism, which switches arm 11% to terminal 136. The resulting decreased resistances eliminate the cold starting enrichment. Passage 1M applies the low manifold pressure to diaphragm N0 of vacuum motor we so diaphragm 1110 moves tap lllb a short distance away from the grounded terminal of element 122. This increased resistance appearing at tenninal it produces a rich mixture for cold engine idling and operation. Threaded screw Mitt is adjusted to determine the portion of intake manifold pressure applied to vacuum motor lltiti, which thereby determines the proper amount of idling fuel. Throttle plate 24 is opened slightly by fast idle cam member to according to the setting of the temperature responsive choke mechanism.

As the engine warms up during continued operation, choke plate 34 opens slowly. This opening decreases the vacuum signal sensed by vacuum motor 108 which moves tap 118 to a lower resistance point that leans the fuel-air mixture accordingly.

During engine road load operation, air valve 30 is positioned by the mass of air flowing through air passage 16 so a relatively constant pressure exists in passage 16 between the air valve and the throttle blade. The opening movement increases the resistance between tap 128 and ground and thereby increases the width of the pulses appearing at terminal fit. When high power is demanded from the engine, the increased intake manifold pressure is applied to diaphragm 74 and moves tap 82 into a high resistance position that increases the pulse width accordingly.

Frictional forces associated with the air valve may produce some hysteresis in response of the air valve to mass airflow.

' Such hysteresis produces variations in the pressure between the air valve and the throttle blade, which are compensated by vacuum motor 108. Vacuum motor 72 and variable resistor M are adjusted so the low intake manifold pressure occurring during engine deceleration moves tap 82 to the lead 87 side of resistor element d6. Lead 138 then has a reduced resistance to ground which prevents transistor from switching to its nonconducting state. No fuel reaches the engine combustion chambers under these conditions, which eliminates undesirable components from the engine exhaust.

Resistor elements 131 can be connected in series with resistor elements 86 and 122 if desired. Variable resistors can be included in leads 138 and M8 to provide desired adjustment. A temperature sensitive variable resistance can be used as resistance 137 to proportion the amount of cold starting fuel to provide to provide excellent cold starting characteristics. The system can be modified so pulse width varies as a function of one electrical signal and pulse height as a function of the others. Fuel injectors then are designed to deliver fuel in response to pulse width and height. Alternatively, pulse width can be decreased with engine speed to compensate for the increased pulse frequency, and fuel metering can be determined by pulse height only.

Thus this invention provides an electronic fuel injection system that uses an air valve to sense the mass of air being inducted into the engine and determine the width of pulses applied to fuel injectors. Vacuum motors sensitive to pressure signals in the intake manifold and in the air induction passage between the air valve and throttle blade adjust fuel delivery for idling and maximum power, and cutoff fuel delivery during deceleration to improve exhaust emission control Injector pulses are synchronized with engine revolutions and electronic circuitry removes the effect of increasing pulse frequency on fuel delivery so fuel delivery is determined only by climate and engine operating parameters.

We claim:

1. ln a fuel injection system for a reciprocating internal combustion engine having at least one electrically operated fuel injector for delivering fuel to a combustion chamber, an air passage for delivering air to said combustion chamber, and a throttle blade in said air passage for controlling the amount of airflow through the air passage, an electronic fuel control system comprising:

an air valve in said air passage upstream of said throttle blade, said air valve being positioned by mass airflow through the passage so air valve position represents the mass of air flowing through the passage,

an electrical device attached to said air valve for converting the air valve position into an electrical signal representative of the mass airflow through the passage,

an air valve depression sensing device connected to the air passage between the air valve and the throttle blade for sensing the pressure therein,

an electrical device connected to the air valve depression device for converting the pressure into an electrical signa representative of the air valve depression, and

electronic means connected to said electrical devices and said injector for controlling the amount of fuel delivered by each operation of the injector as a function of said electrical signals.

2. The fuel injection system or claim 1 in which the electronic means comprises:

pulse generating means for producing a pulse representative of engine rotation, and

pulse forming means for changing the pulse shape according to said electrical signal generated by the air valve position, said pulses being applied to said fuel injector to open and close the injector.

3. The fuel injection system of claim 2 in which the pulse forming means comprises:

a power supply circuit coupled to said pulse generating means, said power supply circuit producing an output voltage inversely proportional to the frequency of the pulses, and

a pulse shaping circuit coupled to the pulse generating means, the power supply circuit and the electrical means attached to the air valve, said pulse shaping circuit producing a pulse having its width proportional to the output voltage of the power supply circuit and the electrical signal of said electrical means.

4. The fuel injection system of claim 3 comprising a manifold pressure sensing device connected to the air passage downstream of the throttle blade for sensing the pressure therein, and an electrical device connected to said manifold pressure sensing device for converting said pressure into an electrical signal representative of manifold pressure, said electrical signal representative of manifold pressure being coupled to said pulse shaping circuit to modify the width of the pulses produced thereby.

5. The fuel injection system of claim 4 in which the air valve depression sensing device also is connected to the air passage downstream of the throttle blade and the electrical signal of said air valve depression sensing device is representative of a predetermined blend of manifold pressure and air valve depression.

6. The fuel injection system of claim 5 in which said electrical devices are variable resistors and the resistance generated by the variable resistor connected to the air valve depression sensing device is coupled in series with the resistance generated by the variable resistor connected to the manifold pressure sensing device.

7. The fuel injection system of claim 6 comprising an electrical resistor means, and a switch means for switching said resistor means into and out of connection with said electrical device attached to said air valve, and temperature responsive means for actuating said switch means, said resistor means being connected to said electrical device at low temperatures to increase the amount of fuel delivered by said injector.

8. The fuel injection system of claim 1 comprising a manifold pressure sensing device connected to the air passage downstream of the throttle blade for sensing the pressure herein, and an electrical device connected to said manifold pressure sensing device for converting said pressure into an electrical signal representative of manifold pressure, said electrical signal representative of manifold pressure being coupled to said electronic means to modify the amount of fuel delivered according to the manifold pressure.

9. The fuel injection system of claim 8 in which the electrical signal generated by the low manifold pressure representative of engine deceleration reduces the amount of fuel delivered by each operation of the injector.

10. The fuel injection system of claim 1 in which said electrical devices are variable resistors.

11. The fuel injection system of claim 1 comprising an electrical resistor means, and a switch means for switching said resistor means into and out of connection with said electrical device attached to said air valve, and temperature responsive means being connected to said electrical device at low temperatures to increase the amount of fuel delivered by said injector.

12. A fuel metering system for an internal combustion engine comprising an air passage for delivering air to said engine, said air passage containing an air valve positioned by the mass of air flowing through said passage and a manually operable throttle valve, said throttle valve being located downstream of the air valve, an electrical device attached to said air valve for converting the air valve position into a first electrical signal, vacuum motor means communicating with said air passage downstream of said throttle blade, said vacuum motor means being responsive to the intake manifold pressure of said engine, an electrical device attached to said vacuum motor means for convening the intake manifold pressure into a second electrical signal, the electronic means for controlling the amount of fuel metered to said engine as a function of said first and second electrical signals, said electronic means including a circuit for producing pulses at a frequency proportional to engine revolutionary speed and a circuit for shortening the duration of said pulses as a function of pulse frequency so the time integrated pulse area is independent of engine revolutionary speed, said electronic means changing pulse area according to said first and second electrical signals.

13. The fuel metering system of claim 1?. comprising a second vacuum motor means communicating with said air passage between said air valve and said throttle valve, and an electrical device attached to said second vacuum motor means for producing a third electrical signal, said electronic means controlling the amount of fuel metered to said engine as a function of said three electrical signals.

14. The fuel metering system of claim 13 in which the electrical devices are variable resistors.

15. The fuel metering system of claim 14 comprising passage means connecting said second vacuum motor means with the air passage downstream of the throttle valve, and manually positionable control means in said passage means for adjusting the proportion of the vacuum signal passing through said passage means to said second vacuum motor. 

2. The fuel injection system or claim 1 in which the electronic means comprises: pulse generating means for producing a pulse representative of engine rotation, and pulse forming means for changing the pulse shape according to said electrical signal generated by the air valve position, said pulses being applied to said fuel injector to open and close the injector.
 3. The fuel injection system of claim 2 in which the pulse forming means comprises: a power supply circuit coupled to said pulse generating means, said power supply circuit producing an output voltage inversely proportional to the frequency of the pulses, and a pulse shaping circuit coupled to the pulse generating means, the power supply circuit and the electrical means attached to the air valve, said pulse shaping circuit producing a pulse having its width proportional to the output voltage of the power supply circuit and the electrical signal of said electrical means.
 4. The fuel injection system of claim 3 comprising a manifold pressure sensing device connected to the air passage downstream of the throttle blade for sensing the pressure therein, and an electrical device connected to said manifold pressure sensing device for converting said pressure into an electrical signal representative of manifold pressure, said electrical signal representative of manifold pressure being coupled to said pulse shaping circuit to modify the width of the pulses produced thereby.
 5. The fuel injection system of claim 4 in which the air valve depression sensing device also is connected to the air passage downstream of the throttle blade and the electrical signal of said air valve depression sensing device is representative of a predetermined blend of manifold pressure and air valve depression.
 6. The fuel injection system of claim 5 in which said electrical devices are variable resistors and the resistance generated by the variable resistor connected to the air valve depression sensing device is coupled in series with the resistance generated by the variable resistor connected to the manifold pressure sensing device.
 7. The fuel injection system of claim 6 comprising an electriCal resistor means, and a switch means for switching said resistor means into and out of connection with said electrical device attached to said air valve, and temperature responsive means for actuating said switch means, said resistor means being connected to said electrical device at low temperatures to increase the amount of fuel delivered by said injector.
 8. The fuel injection system of claim 1 comprising a manifold pressure sensing device connected to the air passage downstream of the throttle blade for sensing the pressure therein, and an electrical device connected to said manifold pressure sensing device for converting said pressure into an electrical signal representative of manifold pressure, said electrical signal representative of manifold pressure being coupled to said electronic means to modify the amount of fuel delivered according to the manifold pressure.
 9. The fuel injection system of claim 8 in which the electrical signal generated by the low manifold pressure representative of engine deceleration reduces the amount of fuel delivered by each operation of the injector.
 10. The fuel injection system of claim 1 in which said electrical devices are variable resistors.
 11. The fuel injection system of claim 1 comprising an electrical resistor means, and a switch means for switching said resistor means into and out of connection with said electrical device attached to said air valve, and temperature responsive means being connected to said electrical device at low temperatures to increase the amount of fuel delivered by said injector.
 12. A fuel metering system for an internal combustion engine comprising an air passage for delivering air to said engine, said air passage containing an air valve positioned by the mass of air flowing through said passage and a manually operable throttle valve, said throttle valve being located downstream of the air valve, an electrical device attached to said air valve for converting the air valve position into a first electrical signal, vacuum motor means communicating with said air passage downstream of said throttle blade, said vacuum motor means being responsive to the intake manifold pressure of said engine, an electrical device attached to said vacuum motor means for converting the intake manifold pressure into a second electrical signal, the electronic means for controlling the amount of fuel metered to said engine as a function of said first and second electrical signals, said electronic means including a circuit for producing pulses at a frequency proportional to engine revolutionary speed and a circuit for shortening the duration of said pulses as a function of pulse frequency so the time integrated pulse area is independent of engine revolutionary speed, said electronic means changing pulse area according to said first and second electrical signals.
 13. The fuel metering system of claim 12 comprising a second vacuum motor means communicating with said air passage between said air valve and said throttle valve, and an electrical device attached to said second vacuum motor means for producing a third electrical signal, said electronic means controlling the amount of fuel metered to said engine as a function of said three electrical signals.
 14. The fuel metering system of claim 13 in which the electrical devices are variable resistors.
 15. The fuel metering system of claim 14 comprising passage means connecting said second vacuum motor means with the air passage downstream of the throttle valve, and manually positionable control means in said passage means for adjusting the proportion of the vacuum signal passing through said passage means to said second vacuum motor. 